Investigation of station inclusion on Disturbance Storm Time (Dst) Index

The Disturbance Storm Time (Dst) Index is used as a global indicator of low and mid-latitude geomagnetic activity. The commonly-used Dst index is based on the measurements from four stations. In this study, a 12-station index is calculated and used as a standard to explore the behavior of Earth's magnetic field under varying geomagnetic conditions. Various Dst indices were calculated, composed of 2, 4, 6, 8, and 10 stations and compared to the 12-station standard. The analysis showed strong agreement for normal and severe geomagnetic storming conditions for all indices. However, during minor geomagnetic storming, Dst less than -50 but greater than -100, the correlations of indices to the 12-station index break down when fewer stations are used. The cause of weaker correlation is attributed to the scale size of the magnetic variation and the longitudinal distribution of the stations. The scale size of the disturbed magnetic field during minor geomagnetic storming conditions is sufficiently small such that not all stations measure the disturbance before dissipation. The favored location for detecting the magnetic variations is near the dusk sector.